U.S. patent application number 17/270394 was filed with the patent office on 2021-12-16 for internal combustion engine for a motor vehicle, having a control unit for aligning a camshaft and method for operating such an internal combustion engine.
This patent application is currently assigned to Daimler AG. The applicant listed for this patent is Daimler AG. Invention is credited to Johannes ERNST, Franz HUBER, Jochen HUFENDIEK, Christian LORENZ, Tilmann ROEMHELD, Frank STRAUSS, Ruediger WEISS, Hardy WEYMANN.
Application Number | 20210388741 17/270394 |
Document ID | / |
Family ID | 1000005866572 |
Filed Date | 2021-12-16 |
United States Patent
Application |
20210388741 |
Kind Code |
A1 |
ERNST; Johannes ; et
al. |
December 16, 2021 |
Internal Combustion Engine for a Motor Vehicle, Having a Control
Unit for Aligning a Camshaft and Method for Operating Such an
Internal Combustion Engine
Abstract
An internal combustion engine for a motor vehicle includes a
crankshaft, a camshaft, a cylinder, a piston movably disposed in
the cylinder and coupled to the crankshaft for driving the
crankshaft, a first gas exchange valve which is assigned to the
cylinder, a first valve clearance compensation device, where via
the first valve clearance compensation device the first gas
exchange valve is displaceable between a first open position and a
first closed position by a first cam of the camshaft, and a control
unit. The control unit is configured to align the camshaft such
that the first valve clearance compensation device is
pressure-loaded in the idle state of the crankshaft by a plateau
area assigned to the first cam to hold the first gas exchange valve
in the first open position.
Inventors: |
ERNST; Johannes;
(Baden-Baden, DE) ; HUBER; Franz; (Kirchheim,
DE) ; HUFENDIEK; Jochen; (Stuttgart, DE) ;
LORENZ; Christian; (Fellbach, DE) ; ROEMHELD;
Tilmann; (Waiblingen, DE) ; STRAUSS; Frank;
(Notzingen, DE) ; WEISS; Ruediger; (Winnenden,
DE) ; WEYMANN; Hardy; (Oberndorf, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Daimler AG |
Stuttgart |
|
DE |
|
|
Assignee: |
Daimler AG
Stuttgart
DE
|
Family ID: |
1000005866572 |
Appl. No.: |
17/270394 |
Filed: |
August 8, 2019 |
PCT Filed: |
August 8, 2019 |
PCT NO: |
PCT/EP2019/071292 |
371 Date: |
February 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01L 1/24 20130101; F01L
13/08 20130101; F01L 1/047 20130101; F01L 1/08 20130101 |
International
Class: |
F01L 1/24 20060101
F01L001/24; F01L 1/047 20060101 F01L001/047; F01L 1/08 20060101
F01L001/08; F01L 13/08 20060101 F01L013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2018 |
DE |
10 2018 006 666.6 |
Claims
1.-6. (canceled)
7. An internal combustion engine for a motor vehicle, comprising: a
crankshaft; a camshaft; a cylinder; a piston movably disposed in
the cylinder and coupled to the crankshaft for driving the
crankshaft; a first gas exchange valve which is assigned to the
cylinder; a first valve clearance compensation device, wherein via
the first valve clearance compensation device the first gas
exchange valve is displaceable between a first open position and a
first closed position by a first cam of the camshaft; and a control
unit which is configured to align the camshaft, at least during a
change of state of the crankshaft from an operating state in which
the crankshaft rotates to an idle state in which the crankshaft is
stationary, such that the first valve clearance compensation device
is pressure-loaded in the idle state by a plateau area assigned to
the first cam to hold the first gas exchange valve in the first
open position.
8. The internal combustion engine according to claim 7, wherein the
control unit is configured to align the camshaft such that the
first valve clearance compensation device at least substantially
abuts a central section of the plateau area in the idle state.
9. The internal combustion engine according to claim 7 further
comprising: a second gas exchange valve which is assigned to the
cylinder; and a second valve clearance compensation device, wherein
via the second valve clearance compensation device the second gas
exchange valve is displaceable between a second open position and a
second closed position by a second cam of the camshaft.
10. The internal combustion engine according to claim 9, wherein
the second valve clearance compensation device is in stroke-free
contact with the second cam while the first valve clearance
compensation device is pressure-loaded by the plateau area in the
idle state and the first gas exchange valve is held in the first
open position.
11. The internal combustion engine according to claim 9, wherein
the second gas exchange valve is actuatable by the second cam using
the second valve clearance compensation device such that a
decompression of the cylinder can be effected.
12. A method for operating the internal combustion engine for a
motor vehicle according to claim 7, comprising the step of:
aligning the camshaft by the control unit, at least during the
change of state of the crankshaft from the operating state in which
the crankshaft rotates to the idle state in which the crankshaft is
stationary, such that the first valve clearance compensation device
is pressure-loaded in the idle state by the plateau area assigned
to the first cam to hold the first gas exchange valve in the first
open position.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] The invention relates to an internal combustion engine for a
motor vehicle. A further aspect of the invention relates to a
method for operating an internal combustion engine for a motor
vehicle.
[0002] From DE 10 2016 013 370 A1, an internal combustion engine
device is known, which is provided to perform a direct start,
having several cylinders which each have at least one valve. At
least one of the cylinders is designed as a direct start cylinder.
The internal combustion engine device comprises at least one valve
train device which is provided to actuate the valves of at least
one cylinder in a first position with a first valve stroke, and in
a second position at least with a second valve stroke designed as a
decompression stroke. The valve train device is provided to form
different decompression strokes for the valves of different
cylinders.
[0003] US 2006/0016411 A1 describes a system for stopping an engine
shaft in a combustion engine after the combustion engine has been
stopped at a predetermined angular position of the shaft with
respect to the engine valves. The system comprises a sensor for
detecting the angular position of the shaft, a programmable
electronic motor control module in electrical connection with the
sensor, and a shaft positioning mechanism responsive to the motor
control module to cause the shaft to stop at the predetermined
angular position.
[0004] From DE 103 42 703 B4, a method for starting a
multi-cylinder internal combustion engine is known. When a starting
process is requested, the position of at least one piston in at
least one associated cylinder is determined, wherein fuel is
injected into a combustion chamber of the cylinder or cylinders of
the piston, which is or are in the working cycle, and wherein a
fuel/gas mixture is ignited in the at least one cylinder which is
in the working cycle, and the piston or pistons of the further
cylinder are set in a forward movement via a crankshaft coupling
the pistons. In at least one cylinder located in a compression
stroke, a decompression valve is opened to reduce the resistance of
the movement of the pistons.
[0005] The object of the present invention is to create an internal
combustion engine and a method of the type mentioned above, by
means of which a particularly low-effort starting of the internal
combustion engine from standstill can be achieved.
[0006] A first aspect of the invention relates to an internal
combustion engine for a motor vehicle, having a crankshaft, having
a camshaft, having a first cylinder, in which a first piston of the
internal combustion engine coupled to the crankshaft for driving
the latter is moveably accommodated, having a first gas exchange
valve which is associated with the first cylinder, having a
hydraulic, first valve clearance compensation device via which the
first gas exchange valve can be displaced between a first open
position and first closed position by means of a first cam of the
camshaft. The camshaft can be coupled directly or indirectly to the
crankshaft and can thus be driven via the crankshaft. The first gas
exchange valve can be formed as a first inlet valve, through which
fresh air can flow from at least one inlet channel of the internal
combustion engine into a first combustion chamber, which is at
least partially limited by the first cylinder and the first piston.
The hydraulic, first valve clearance compensation device can
generally also be abbreviated as first HVA.
[0007] In order to enable a particularly low-effort starting of the
internal combustion engine from standstill, it is provided in
accordance with the invention that the internal combustion engine
comprises a control unit which is set up to control at least one
change of state of the crankshaft from an operating state in which
the crankshaft rotates, into an idle state in which the crankshaft
is stationary, to align the camshaft in such a way that the first
valve clearance compensation device is pressure-loaded in the idle
state by means of a plateau area assigned to the first cam, which
is designed as a plateau cam, and thereby holds the first gas
exchange valve in the first open position. This is advantageous
since, due to the first open position of the first gas exchange
valve, which is pressure-loaded and correspondingly depressed by
the plateau area of the first cam ("plateau cam") of the camshaft
when the internal combustion engine is started (when the crankshaft
accelerates from its resting state into the operating state), an at
least partial intake of gas or combustion air from the first
cylinder via the gas exchange valve located in the first open
position can occur, whereby a correspondingly low torque of the
first cylinder prevents the starting of the internal combustion
engine. In other words, the torque which makes starting the
internal combustion engine more difficult, for example when
compressing the gas contained in the first cylinder in a
compression stroke, can be avoided, whereby starting the internal
combustion engine from standstill can occur in a correspondingly
simple and low-effort manner. Furthermore, it is particularly
advantageous that the pressure loading of the first valve clearance
compensation device at least largely or even completely prevents a
torque loading on the camshaft by means of the plateau area of the
first cam when the internal combustion engine is at a standstill
(and thus in the idle state of the crankshaft). In other words,
ideally no torque is applied to the camshaft from the first cam of
the first cylinder when the hydraulic first valve clearance
compensation device is pressure-loaded by means of the plateau area
of the first cam.
[0008] The plateau area is to be understood as an area of the first
cam which is at least substantially flat and thus at least largely
gradient-free. Preferably, the gradient of a cam contour of the
first cam on the plateau area is the value "0" at least in one
plateau zone of the plateau area. In other words, the cam contour
on the plateau zone is preferably flat and therefore without
gradient. The plateau area can therefore preferably be shaped in
such a way that, at least in the plateau zone, there is no change
in the lift of the first gas exchange valve, as long as the first
cam on its plateau area, in particular in the plateau zone, acts on
the hydraulic, first valve clearance compensation device, i.e.,
pressure-loads the latter. The plateau area can preferably be as
wide as possible, wherein the plateau zone can extend over a crank
angle of 85.degree. KW, for example. The plateau zone extends over
a crank angle range of from 415.degree. KW to 500.degree. KW,
wherein the respective work cycles (intake cycle, compression
cycle, combustion cycle, exhaust cycle) extend over two complete
rotations of the crankshaft, i.e., over a range of from 0.degree.
KW to 720.degree. KW. Preferably, the plateau zone extends over a
crank angle of 65.degree. KW in a crank angle range of from
435.degree. KW to 500.degree. KW.
[0009] Due to the plateau area, the first gas exchange valve as a
whole can be held in the first open position in the area of the
expected shutdown position of the internal combustion engine, i.e.,
the expected crankshaft position of the crankshaft at constant
stroke, such that, due to the open (in the first open position)
first gas exchange valve at standstill, as little torque as
possible acts on the camshaft. This also contributes to a
particularly low-effort starting of the internal combustion
engine.
[0010] In an advantageous development of the invention, the control
unit is set up to align the camshaft in such a way that the first
valve clearance compensation device in the idle state of the
crankshaft at least substantially abuts a central portion of the
plateau area of the first cam. This is advantageous because it
prevents any backward or forward swinging of the camshaft and
crankshaft during shutdown and instead allows a defined respective
position of the camshaft and crankshaft to be assumed and
maintained.
[0011] In a further advantageous development of the invention, the
internal combustion engine comprises a second gas exchange valve
which is assigned to the first cylinder, and a hydraulic, second
valve clearance compensation device by means of which the second
gas exchange valve can be displaced between a second open position
and a second closed position by means of a second cam of the
camshaft. The second gas exchange valve can be designed as a second
inlet valve. This is advantageous because the second gas exchange
valve can be used in addition to the first gas exchange valve to
enable a particularly demand-oriented charge exchange in the first
cylinder.
[0012] The first cam is designed as a "plateau cam" and can
preferably be designed alongside a third cam, a so-called "filling
cam", wherein the first cam has a lower valve stroke overall than
the third cam. The third filling cam enables the first cylinder to
be filled with a particularly large quantity (mass flow) of fresh
air, which is available for combustion and shifts the first gas
exchange valve between a third open position and a third closed
position. The third cam ("filling") corresponds to the known cams
for inlet valves for the combustion operation. The first cam
("plateau"), on the other hand, is used in particular to reduce the
torque of the first cylinder during starting and to fill the first
cylinder with sufficient fresh air for a combustion operation in
the low load range and/or at low rotational speeds and includes the
plateau area for a torque-free shutdown of the internal combustion
engine. By means of the third cam, the first gas exchange valve can
be shifted to the third open position during fired operation of the
internal combustion engine in order to cause a favorable inflow of
the desired amount of fresh air for fuel combustion. Towards higher
loads and/or rotational speeds, it is possible to switch over from
the first cam to the third cam and operate the first gas exchange
valve accordingly.
[0013] Alongside the second cam, a further, fourth cam is provided.
The fourth cam is designed as a "filling cam" analogous to the
third cam and is switched over to higher rotational speeds with the
third cam after the starting operation or a combustion operation
with a low rotational speed. The fourth cam has a fourth open
position and a fourth closed position, which is designed
analogously to the third open position and third closed
position.
[0014] Switching over from the first cam (plateau) and from the
second cam (decompression) to the respective adjacent third cam and
fourth cam (filling) can be done at a rotational speed in the range
of 1000 rpm of the internal combustion engine.
[0015] In a further advantageous development of the invention, the
second valve clearance compensation device on the second cam is in
stroke-free contact, while the first valve clearance compensation
device is pressure-loaded by means of the plateau area in the idle
state and thus the first gas exchange valve is held in the first
open position. In other words, the hydraulic, second valve
clearance compensation device (HVA) is not pressurized by the
second cam in such a way that the second valve clearance
compensation device opens the second gas exchange valve, i.e.,
moves it into a second open position assigned to the second gas
exchange valve or holds it in this open position. The second valve
clearance compensation device (HVA) is located in the shutdown
position of the internal combustion engine in the area of a base
circle of the second cam, which means that the second gas exchange
valve remains in its second closed position while the first gas
exchange valve remains in its first open position.
[0016] This is based on the knowledge that the first HVA or the
second HVA is usually designed as a spring-operated compensating
piston and can be arranged between the respective gas exchange
valves and, if necessary, other valve actuation devices which are
known per se and operated by the respective cams, which may include
rocker arms, drag levers, cup tappets and the like. The
compensating piston is extended by means of a spring force of the
spring and reduces a valve clearance of the respective gas exchange
valves to the value "zero" during engine running (operation) of the
internal combustion engine. The retraction of the compensating
piston is delayed in a controlled manner by means of engine oil
drawn in when the compensating piston is extended and by means of a
check valve. When the engine is at a standstill (idle state of the
crankshaft) and the respective gas exchange valve is open (for
example, in the first open position of the first gas exchange
valve), the engine oil is at least partially pressed out of the
respective HVA (for example from the hydraulic, first valve
clearance compensation device) and the respective gas exchange
valve moves in the direction of a valve seat assigned to it (in
which the respective gas exchange valve is in its closed position).
If one of the respective gas exchange valves is in a respective
filling or intake phase of the first cylinder during engine
standstill, i.e., the first cam acts with its plateau area on the
first gas exchange valve, the respective, smaller valve stroke of
the first cam is further reduced compared to a valve stroke of the
third filling cam of the respective gas exchange valve, wherein the
respective gas exchange valve is nevertheless not completely
closed. The valve stroke of the first gas exchange valve in the
first open position during engine standstill is then smaller than
the valve stroke of the first gas exchange valve in the first open
position in the combustion operation, but remains open. When the
engine is restarted (acceleration of the crankshaft from idle state
to operating mode), a torque of the first cylinder preventing the
engine start is reduced, which facilitates the starting
process.
[0017] In a further advantageous development of the invention, the
second gas exchange valve can be operated by means of the second
cam using the second valve clearance compensation device in such a
way that a decompression of the first cylinder can be effected.
This is advantageous, since this allows a filling and a
decompression of the first cylinder to be distributed to several
valve trains with correspondingly two gas exchange valves per
cylinder. In this way, it is possible to adjust the filling and
decompression settings in a particularly flexible manner.
[0018] The second cam can be designed as a "decompression cam" with
a decompression valve lift, wherein the decompression valve lift
can cause a smaller valve stroke of the second gas exchange valve
than is the case with the plateau area of the first cam. The
decompression valve lift can be positioned between the bottom dead
center (BDC) of the first piston and its top ignition dead center
(TDC) as close as possible to a maximum piston speed of the first
piston, since the largest piston path of the first piston and thus
the highest possible compression ratio takes place in this area. A
maximum value of the decompression valve stroke can preferably be
less than 3.0 mm, and an opening width (elevation width) of a cam
elevation of the second cam can preferably be a value of less than
180.degree. KW. The second gas exchange valve can preferably be
closed in the shutdown position of the internal combustion engine
(idle state and idle position of the crankshaft), such that an
unfavorable compression of the second HVA is prevented. The first
gas exchange valve and the second gas exchange valve have different
open and closed positions, wherein in the first open position of
the first gas exchange valve, the second gas exchange valve is in
the second closed position, and in the second open position of the
second gas exchange valve, the first gas exchange valve is in the
first closed position.
[0019] The first cam ("plateau cam") can favorably enable the
internal combustion engine to output power with the combustion as
the rotational speed of the crankshaft increases, for example from
rotational speed values of the rotational speed of greater than or
equal to 500 rpm. Here, the second cam ("decompression cam") is not
intended to support the filling of the combustion chamber of the
first cylinder, but only to effect decompression at low rotational
speeds, for example at rotational speed values of the rotational
speed below 500 rpm.
[0020] This can be achieved in a particularly advantageous way by
designing the small "decompression cam" (second cam) with regard to
its stroke in such a way that it does not stall at low rotational
speeds (low rotational speeds of the crankshaft) in towing
operation of the internal combustion engine due to low speeds of
the gas flowing out of the first cylinder during the charge
exchange, on the other hand, it stalls with increasing engine speed
(higher rotational speeds of the crankshaft) due to the increasing
speeds (of the gas) and thus a cylinder filling flowing out again
(due to the outflowing gas) becomes correspondingly smaller. The
"plateau cam" is designed in such a way that no supercritical
pressure conditions occur and the cylinder filling is substantially
maintained even with increasing engine speed. As a result, a
combustion is achieved with increasing torque output from the
crankshaft of the internal combustion engine with increasing engine
speed (rotational speed of the crankshaft).
[0021] A second aspect of the invention relates to a method for
operating an internal combustion engine for a motor vehicle, which
comprises a crankshaft, a camshaft, a first cylinder in which a
first piston of the internal combustion engine coupled to the
crankshaft for driving the latter is moveably accommodated, as well
as a first gas exchange valve associated with the first cylinder
and a hydraulic, first valve clearance compensation device via
which the first gas exchange valve can be displaced between a first
open position and a first closed position by means of a first cam
of the camshaft.
[0022] According to the invention, the internal combustion engine
comprises a control unit, by means of which, at least during a
change of state of the crankshaft from an operating state in which
the crankshaft rotates into an idle state in which the crankshaft
is stationary, the camshaft is aligned in such a way that the first
valve clearance compensation device is pressure-loaded in the idle
state by means of a plateau area assigned to the first cam designed
as a plateau cam, and the first gas exchange valve is thereby held
in the first open position. The features presented in connection
with the internal combustion engine according to the first aspect
of the invention as well as their advantages apply accordingly to
the method according to the second aspect of the invention and vice
versa.
[0023] Further advantages, features and details of the invention
emerge from the following description of a preferred exemplary
embodiment and from the drawings. The features and combinations of
features mentioned above in the description as well as the features
and combinations of features mentioned in the following description
of the figures and/or shown in the figures alone cannot only be
used in the combination specified in each case, but also in other
combinations or on their own without leaving the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a diagram which shows a valve stroke course of a
first gas exchange valve as well as a second gas exchange valve
over a crank angle course of a crankshaft of an internal combustion
engine, wherein the first gas exchange valve and the second gas
exchange vale are assigned to a first cylinder of the internal
combustion engine;
[0025] FIG. 2 is a further diagram which shows the respective valve
stroke course of the first and second gas exchange valve and a
respective mass of air flowing into the first cylinder and air
flowing out via the crank angle course of the crankshaft during a
charge exchange at a rotational speed of the crankshaft of less
than 500 rpm;
[0026] FIG. 3 is a further diagram which shows a speed of the air
flowing into the first cylinder and the air flowing out via the
crank angle course of the crankshaft during charge exchange at a
rotational speed of the crankshaft of less than 500 rpm;
[0027] FIG. 4 is a further diagram which shows the respective valve
stroke course of the first and second gas exchange valve and the
respective masses of air flowing into the first cylinder and air
flowing out via the crank angle course of the crankshaft during the
charge exchange at a rotational speed of the crankshaft of greater
than or equal to 500 rpm; and
[0028] FIG. 5 is a further diagram which shows the speed of the air
flowing into the first cylinder and the air flowing out via the
crank angle course of the crankshaft during charge exchange at the
rotational speed of the crankshaft of greater than or equal to 500
rpm.
DETAILED DESCRIPTION OF THE DRAWINGS
[0029] FIGS. 1 to 5 serve to illustrate an operation of an internal
combustion engine not depicted in more detail here for a motor
vehicle also not depicted in more detail here. The internal
combustion engine comprises a crankshaft, a camshaft, a first
cylinder in which a first piston of the internal combustion engine
coupled to the crankshaft for driving the latter is moveably
accommodated, a first gas exchange valve which is assigned to the
first cylinder, a hydraulic, first valve clearance compensation
device via which the first gas exchange valve can be displaced
between a first open position and a first closed position by means
of a first cam of the camshaft.
[0030] In addition, the internal combustion engine comprises a
control unit which is set up to align the camshaft, at least during
a change of state of the crankshaft from an operating state in
which the crankshaft rotates to a rest state in which the
crankshaft is stationary, in such a way that the first valve
clearance compensation device is pressure-loaded in the idle state
by means of a plateau area 11 assigned to the first cam, and thus
the first gas exchange valve is held in the first open position.
The first cam is designed as a plateau cam.
[0031] The control unit is set up to align the camshaft in such a
way that the first valve clearance compensation device at least
substantially abuts a central section 13 of the plateau area 11 in
the idle state of the crankshaft.
[0032] In addition, the internal combustion engine comprises a
second gas exchange valve, which is assigned to the first cylinder,
and a hydraulic, second valve clearance compensation device, via
which the second gas exchange valve can be displaced between a
second open position and a second closed position by means of a
second cam of the camshaft.
[0033] The second valve clearance compensation device is in
stroke-free contact with the second cam, while the first valve
clearance compensation device is pressure-loaded by means of the
plateau area 11 in the idle state, and thus the first gas exchange
valve is held in the first open position. The second gas exchange
valve can be actuated by means of the second cam using the second
valve clearance compensation device in such a way that a
decompression of the first cylinder can be effected. The second cam
is designed as a decompression cam.
[0034] The internal combustion engine is designed in this case to
perform a so-called "direct start" with particularly low effort,
i.e., to start the internal combustion engine solely by combustion
energy and thus to accelerate the crankshaft from the idle state to
the operating state solely by combustion energy. Furthermore, the
internal combustion engine is suitable for a conventional start by
means of a starter or an electric motor, for example. The internal
combustion engine according to the invention is particularly
suitable for starting a hybrid motor vehicle without load.
[0035] In order to carry out the start and in particular the direct
start, i.e., the starter-free acceleration (acceleration without
starter) of the crankshaft of the internal combustion engine from
the idle state to the operating state, the crankshaft is shifted
from the operating state to the idle state before the direct start,
and in doing so, is stopped by means of the control unit in a
position (crankshaft position) in relation to the first cam
("plateau cam") in such a way that a valve actuation (rocker arm,
drag lever, cup tappet etc.) is shut down approximately in the
center or in a central section 13 of the plateau area 11 and thus
in a plateau zone of the plateau area 11, where it results in a
constant stroke 10 of the first gas exchange valve. In FIG. 1, this
is the case in a crank angle range between approximately
435.degree. KW and 500.degree. KW (crank angle). A corresponding
valve stroke course 12 in the combustion operation is plotted as a
dashed line in a diagram in FIG. 1, which shows the valve stroke
h.sub.V over the crank angle .degree. KW. The valve stroke course
has a corresponding plateau area 11 with its central section 13.
The first open position of the first gas exchange valve is
substantially between the gas exchange OT (GWOT) at about
360.degree. KW and shortly after the bottom dead centre (BDC) at
about 570.degree. KW. In this way, the first gas exchange valve,
which is designed as the first inlet valve of the first cylinder,
is opened (in the first open position) when the internal combustion
engine is shut down (idle state of the crankshaft), and thus
compresses the first valve clearance compensation device (first
HVA), i.e., in other words pressure-loads it, whereby the first HVA
is out of operation. This means that, after the internal combustion
engine has been shut down, a valve stroke of the first gas exchange
valve is smaller than the stroke 10 by the amount of the compressed
first valve clearance compensation device. This does not pose a
problem for starting the internal combustion engine in the form of
direct starting, since the first inlet valve remains wide open
during the intake stroke despite compressed first HVA.
[0036] Furthermore, by shutting down the internal combustion engine
in such a way that the first HVA is depressed (pressure-loaded) by
the plateau area 11 and thus the first gas exchange valve is held
in the first open position, no compression-related torque is
introduced via the camshaft into the crank drive and thus the
crankshaft, especially as the first gas exchange valve does not act
or press on any flank of the first cam via the valve actuation.
Overall, any backward or forward swinging of the crankshaft of the
internal combustion engine during shutdown can be avoided and a
defined position of the camshaft and the crankshaft can be
assumed.
[0037] The valve actuation of the first gas exchange valve
resulting from the kinematic coupling of the camshaft or the first
cam and the first HVA supports the starting (direct start) of the
internal combustion engine, i.e., the acceleration of the
crankshaft from its idle state at the transition from the plateau
area 11 to a falling flank of the first cam, such that the
acceleration of the crankshaft can take place with an introduction
of a torque via the camshaft to the crankshaft and accordingly the
starting of the internal combustion engine can be designed to be
particularly low-effort.
[0038] The second gas exchange valve, which is designed as a second
inlet valve assigned to the first cylinder, is still closed when
the internal combustion engine is shut down, since the second inlet
valve is only opened between 570 and 630.degree. KW and closed
between 630.degree. KW and 690.degree. KW by means of the second
cam designed as a "decompression cam". As can be seen in FIG. 1 by
means of a valve stroke course 14 assigned to the second inlet
valve, a second open position can substantially occur between
600.degree. KW and 675.degree. KW. The second open position of the
second gas exchange valve only occurs in the first closed position
of the first gas exchange valve. The first open position of the
first gas exchange valve occurs in the second closed position of
the second gas exchange valve.
[0039] The second inlet valve opens for the decompression in the
compaction cycle, i.e., when the first piston is located between
its bottom dead canter (BDC) at 540.degree. KW and its top ignition
dead centre (TDC) at 720.degree. KW, as is also shown in FIG. 1.
The hydraulic, second valve clearance compensation device (second
HVA) of the second inlet valve is therefore unloaded when the
internal combustion engine is switched off and therefore in
operation when the internal combustion engine is restarted (direct
start), especially since no engine oil has been previously forced
out of the hydraulic, second HVA, which allows the decompression of
the (compressing) first cylinder to take place during start/restart
of the internal combustion engine.
[0040] By way of example, if the internal combustion engine is
designed as a 4-cylinder engine having an ignition sequence 1-3-4-2
(first cylinder-third cylinder-fourth cylinder-second cylinder),
the decompression cam (second cam) of the cylinder "2" (second
cylinder) acts on the second inlet valve of this cylinder "2",
since the ignition distance is 180.degree. KW and thus the plateau
area 11 of the first cam ("plateau cam") for the first inlet valve
of the cylinder "1" and the decompression cams (second cam) of the
second inlet valve of the cylinder "2" coincide. Thus, the first
inlet valve of the cylinder "1" is opened (in the first open
position) when the internal combustion engine is switched off by
the plateau area 11 of the "plateau cam" and is fired when the
internal combustion engine is (directly) started, whereby ignitable
fuel-air mixture contained in the first cylinder (cylinder "1") is
ignited, while in cylinder "2" (which is ignited in the fourth
position in the ignition sequence and thus the last of the four
cylinders to be ignited), the corresponding decompression cam acts
on the second inlet valve of the cylinder "2". However, the
negative influence of the compressed, second HVA for this second
inlet valve of the cylinder "2" is negligible for the direct start
of the internal combustion engine, since there is a residual stroke
of this second inlet valve (i.e., there is a decompression effect),
and the cylinder "2" has already been at least partially
decompressed when the internal combustion engine is switched
off.
[0041] If the internal combustion engine is designed as a
6-cylinder engine, for example, this problem does not arise, since
in this case, the ignition distance (between the total of 6
cylinders) is 120.degree. KW, and thus the "filling cam" of the
first cylinder and the "decompression cam" of the second cylinder
coincide.
[0042] After the internal combustion engine has been started, i.e.,
in other words the camshaft from the idle state into the operating
state, the inlet-side valve train is switched over, for example,
when the rotational speed of the internal combustion engine is in
the range of 1000 rpm. In doing so, the first cam and
simultaneously the second cam are switched over to third and fourth
cams respectively arranged in parallel to the two cams, resulting
in an inlet valve stroke course 16 of the first gas exchange valve
and the second gas exchange valve, which is illustrated in FIG. 1
by a solid line.
[0043] An exhaust-side valve train assigned to the first cylinder
remains unaffected, which can be seen in an exhaust valve stroke
course 18 shown in FIG. 1.
[0044] The inlet-side valve train can be operated by means of a
so-called "Camtronic system", for example, and thus the valve
stroke course 12, 14 and/or the inlet valve stroke course 16 can be
varied. Different inlet-side cams are provided for the first and
second inlet valve in a starting or decompression mode with a
plateau cam (with its valve stroke course 12) and a decompression
cam (with its valve stroke course 14) and, for example, two
identical cams without respective plateau or decompression areas
for the normal combustion operation. By way of example, the two
third and fourth cams arranged next to a plateau cam and a
decompression cam are designed as filling cams and each have the
valve stroke course 16.
[0045] FIGS. 2 to 5 show the respective first and second open
positions and the corresponding first and second closing positions
of the first gas exchange valve and the second gas exchange valve
with the respective opening and closing times of the respective
inlet valve stroke courses 12 and 14.
[0046] FIGS. 2 to 5 serve to illustrate that the plateau cam in
conjunction with the decompression cam can cause changed flow
behaviour compared to decompression devices previously known from
the prior art.
[0047] On the respective axes of the diagrams shown in FIG. 2 to
FIG. 5, in addition to the valve stroke h.sub.v and the crank angle
.degree. KW, the integrated mass flow of fresh air in kg, as well
as the speed--expressed by the Mach number Ma--of the gas (air)
flowing during charge exchange, are also specified. In the case of
previously common strokes of decompression devices, gas exchange
valves were opened in each case to such an extent that there was no
or only a slight influence on the flow of the charge of the first
cylinder exiting the combustion chamber.
[0048] With corresponding decompression strokes by means of the
second cam, decompression can be performed at low rotational speeds
(less than 500 rpm, see FIG. 2), as expressed by the valve stroke
course 14. An integrated mass flow 24 is depicted with a solid
line, as generated by the valve stroke course 12 of the plateau
cam. The first gas exchange valve is moved from its first closed
position to its first open position, after which the mass flow 24
increases from zero to a positive value of zero, different from
zero. Subsequently, the first gas exchange valve is moved back into
its first closed position. During the first closed position of the
first gas exchange valve, the second gas exchange valve is moved
from its second closed position to its second open position, after
which a mass flow 26 is generated by the valve stroke course 14 of
the decompression cam, with a negative value different from zero.
Subsequently, the second gas exchange valve is then moved back to
its second closed position. As depicted by the dotted line, a
negative integrated mass flow 26 exits the cylinder again via the
second gas exchange valve. The total mass of fresh air remaining in
the cylinder is the sum of the two mass flows 24 and 26 after the
open position of the second gas exchange valve in its second closed
position. As can be seen in FIG. 3, the valve stroke course 12 of
the first gas exchange valve has a speed course 20 of the inflowing
fresh air. During decompression (valve stroke course 14) by means
of the second cam, the Mach number 1 of the air flowing out of the
cylinder is not reached (course 22). At higher rotational speeds
(greater than 500 rpm), the decompression effect decreases and
compression is carried out in the first cylinder to such an extent
that ignition is possible. As can be seen in FIG. 4, the inflowing
fresh air (mass flow 24) has a similar course as in FIG. 2.
However, the mass flow 26 of the air flowing out of the cylinder
(decompression) generated by the valve stroke lift 14 significantly
decreases. The fresh air remaining in the cylinder increases, such
that a sufficient compression is achieved for a combustion of fuel
in the first cylinder, whereby fuel injected into the first
cylinder can ignite and combust. As can be seen in FIG. 5, the
valve stroke course 12 of the first gas exchange valve has, at
higher rotational speeds, a speed profile 20 of inflowing fresh air
which is higher than at low rotational speeds (FIG. 3). During
decompression (valve stroke course 14) by means of the second cam,
the Mach number 1 is exceeded (course 22). In this case, the flow
is blocked during decompression due to the super critical speed
itself and the mass flow 26 of outflowing fresh air via the second
gas exchange valve of the first cylinder decreases with the same
valve stroke course 14. The integrated mass flows 24 shown in FIGS.
2 and 4 do not change significantly in the example shown at
rotational speeds in the range of 500 rpm.
[0049] The internal combustion engine according to the invention
and the method according to the invention ensure that a
decompression effect is also present after longer standstill
periods of the internal combustion engine.
LIST OF REFERENCE CHARACTERS
[0050] 10 stroke [0051] 11 plateau area [0052] 12 valve stroke
course [0053] 13 central section [0054] 14 valve stroke course
[0055] 16 inlet valve stroke course [0056] 18 exhaust valve stroke
course [0057] 20 speed [0058] 22 speed [0059] 24 mass flow [0060]
26 mass flow
* * * * *